A factory produces cans of mixed nuts. Each can contains x ounces
of peanuts, and twice as many ounces of cashews, almonds, and 
Brazil nuts combined, peanuts cost 15 cents an ounce, and all other 
nuts cost 20 cents an ounce. How do you express the cost of a can of 
nuts in dollars?

There are x oz of peanuts and 2x oz of other nuts.

So the dollar amount is

15 cents TIMES the no. of oz. of peanuts PLUS 20 cents TIMES the no. 
of oz. of other nuts.  

OR

$.15x + $.20(2x)

That simplifies to

$.15x + $.40x

or

$.55x

Edwin